Tensionser pulley / serpentine belt question

[Mkraus01]

I installed the larger tensioner pulley wheel that came with my kit, as well as the FFR supplied serpentine belt. For the life of me, I cannot get the belt over the idler tensioner..... I rotate the tensioner until it bottoms out and the belt is still too short..... I reinstalled the smaller Corvette tensioner pulley wheel and I can get the serpentine belt over it with plenty of tension on the belt....

Is this common, or am I somehow missing something?

The belt is a 6PK1575, the FFR pulley is approximately 3.5” diameter and the corvette pulley is approximately 2.75” diameter.

I appreciate others experiences.

Mike Kraus
Jackson, MI
Built 5 airplanes, but this is my first car!

[VRaptor SpeedWorks, LLC]

I found out "after the fact" that one of the cars that we just completed was like this. The owner of the car installed the engine and belt/tensioner, so I didn't think anything about it. We got the car finished and when we first started the car, I could hear the belt rubbing on the bottom of the waterfall....which I had not experienced before in almost 30 GTM builds. So I pull the waterfall off and find that the belt had worn a groove in the bottom of the waterfall and the tensioner had very little travel left in it. Obviously the belt that was installed wasn't going to work, so I cut it and used it to figure out the ideal belt length and headed to the parts store to see what I could find. Finally found a belt in the length I was looking for and everything worked out. When I mentioned this to the owner, he said, "Oh yeah.....when I was putting that together, the FFR belt wouldn't fit, so I had to go get a longer belt."

Apparently FFR has ended up with a batch of wrong belts or something?

[DaveS53]

The tensioner body should have marks on it that indicate the correct range of tension. As long as it's in range, I wouldn't worry about it, as long as there are no belt clearance issues. With the LS3 that I put in my hot rod, I had the opposite problem. I couldn't get enough tension unless the belt was so tight that it was nearly impossible to install. If I had a .75 inch smaller pulley in the mix, I'd have no tension at all. There is little room for error when it comes to belt length or pulley size. That much diameter difference, with a 40% wrap would require about a 25mm difference in belt length. I've found that only a 5mm difference in length can make a belt too short to install or too long to produce enough tension.

If a larger tensioner pulley was supplied, it would make me think it was done due to eliminate a belt rubbing issue.

One thing that I just remembered about installing a very tight belt - find a way to hold the tensioner fully retracted - I used a long breaker-over bar and a large adjustable turnbuckle, attached to the breaker bar and frame. Slip the belt under the smooth water pump pulley last, then release the tensioner.

[Mkraus01]

Here are my pictures. One shows the routing and smaller tensioner Pulley, other shows the tension.

[DaveS53]

Looks good to me.

[kabacj]

I’ll second that.

I used the same belt route.

No issues with slip under any circumstances.

I have a high torque high rev motor and ended up stiffening up
The bracket that carries the belt tensioning pulley.

The belt would make a little noise under a quick rev. Never any issues however.

A strut keeping the mounting plate from flexing stopped the noise.